This invention relates to a stereocontrolled total synthesis of the known antibiotic thienamycin (I). ##STR3## Starting from acetone dicarboxylate, the synthesis proceeds in a stereo-selective way via intermediate II: ##STR4## wherein R and ##STR5## are readily removable protecting groups; and wherein R and R' are selected, inter alia, from: phenyl; benzyl; 1,1,1-trichloroethyl; methyl; ethyl; t-butyl; and the like.